This invention relates to a riser reactor system comprising a catalyst feed device and a process for the preparation of an olefinic product.
Processes for the preparation of olefins from oxygenates are known in the art. Of particular interest is often the production of light olefins, in particular ethylene and/or propylene. The oxygenate feedstock can for example comprise methanol and/or dimethylether, and an interesting route includes their production from synthesis gas derived from e.g. natural gas or via coal gasification.
For example, WO2007/135052 discloses a process wherein an alcohol and/or ether containing oxygenate feedstock and an olefinic co-feed are reacted in the presence of a zeolite having one-dimensional 10-membered ring channels to prepare an olefinic reaction mixture, and wherein part of the obtained olefinic reaction mixture is recycled as olefinic co-feed. With a methanol and/or dimethylether containing feedstock, and an olefinic co-feed comprising C4 and/or C5 olefins, an olefinic product rich in light olefins can be obtained.
Another oxygenate-to-olefins process is described in WO 2004/037950 A1, wherein an oxygenate feedstock is converted in a riser reactor system having a plurality of parallel risers.
Yet another process for the conversion of oxygenate into olefins is described in WO 01/62689, wherein oxygenate is stagewise injected into a fluidized bed reaction zone.
Moreover it has been shown in International patent applications No. PCT/EP2008/065863 and PCT/EP2008/065872 (both unpublished at the date of filing the present application, and both incorporated herein by reference) that and how oxygenate-to-olefins processes can benefit from staged feeding of the oxygenate feed. In a riser reactor system it is moreover preferable to add catalyst as well.
Applicants have realized that it can be beneficial to stage feed admission in a riser reactor system by adding feed at various heights. However, there seems to be no suitable catalyst inlet device available for this task that allows suitable admission of catalyst into a riser reactor system. At an elevated position in a riser, a flow pattern has developed and should desirably not be significantly disturbed by the addition of further catalyst. The problem is particularly pronounced when it is desired to use a riser reactor system of significant diameter, such as of larger than 0.5 m, larger than 1 m, or even more. A riser reactor as disclosed in U.S. Pat. No. 4,927,522 for a fluidized catalytic cracking (FCC) system does not address these problems. In the known reactor, catalyst is added simply from a side inlet to the riser. The inventors of the present invention have realized that this biases the catalyst towards one side of the reactor and severely disturbs an already existing flow pattern in the reactor.
There is a need for an improved catalyst feed device for riser reactor systems.